Quick Answer: California AB 68 (2020) reduced ADU setbacks statewide to a maximum of 4 feet from rear and side property lines. Cities cannot require setbacks larger than 4 feet for ADUs under 800 sq ft, and many Bay Area cities have adopted exactly the 4-foot minimum. This is a dramatic improvement from pre-2020 rules where many cities required 5–10 foot setbacks, making ADUs infeasible on many smaller lots. ADUs over 800 sq ft may be subject to different setback rules, and attached ADUs must follow standard setback rules of the main structure.
ADU Setback Rules by Bay Area City — 2025
Helpful Resources:
| City | Rear Setback (ADU) | Side Setback (ADU) | Max ADU Size | Notes |
|---|---|---|---|---|
| San Jose | 4 feet | 4 feet | 1,200 sq ft | 4-foot rule applies to detached ADUs under 800 sq ft; larger ADUs may need 5-ft side yard |
| Oakland | 4 feet | 4 feet | 1,200 sq ft | No owner-occupancy requirement; ADU allowed with any SFR or duplex |
| San Francisco | 5 feet (varies) | 5 feet | No size limit (unit size) | SF ADU rules are complex; rear yard preservation also applies |
| Palo Alto | 5 feet | 5 feet | 850 sq ft (attached); 1,200 sq ft (detached) | Palo Alto maintains 5-ft setbacks; JADU allowed up to 500 sq ft |
| Sunnyvale | 4 feet | 4 feet | 1,200 sq ft | Streamlined permit process; many ADUs ministerially approved |
| Fremont | 4 feet | 4 feet | 1,200 sq ft | Standard California minimums apply |
| Berkeley | 4 feet | 4 feet | 1,200 sq ft | Berkeley added ADU streamlining in 2021 |
| Mountain View | 4 feet | 4 feet | 1,200 sq ft | Very ADU-friendly; streamlined ministerial approval |
What ADU Setback Rules Mean for Your Bay Area Lot
The 4-foot ADU setback rule means that a detached ADU can be built as close as 4 feet from the rear and side property lines. For a 50-foot wide lot with a 5-foot side setback on each side, the buildable width for a detached ADU is 50 – 5 – 5 = 40 feet. For a lot with 4-foot setbacks, buildable width is 50 – 4 – 4 = 42 feet. This 4-foot rule opens up ADU possibilities on many Bay Area lots that were previously considered too small or irregular for ADU construction.
Can I build an ADU within 4 feet of my neighbor’s fence in San Jose? Yes — under California law and San Jose’s ADU ordinance, detached ADUs under 800 sq ft can be built with a 4-foot setback from rear and side property lines (the fence line is typically the property line). However, the wall facing within 4 feet of the property line must meet fire-rated construction requirements under California Building Code Section R302 — typically 1-hour fire-rated exterior wall construction (fire-rated drywall, no combustible exterior cladding within 3 feet of the property line). Your ADU contractor must address this in the design.
What is the maximum ADU size in California? California state law sets the maximum ADU size at 1,200 sq ft for a detached ADU, with no minimum lot size requirement for cities with single-family zoning. A Junior ADU (JADU) is limited to 500 sq ft and must be within the existing primary structure. Cities cannot set maximum ADU sizes smaller than 850 sq ft for attached ADUs or 1,200 sq ft for detached ADUs — any local ordinance with smaller caps is preempted by state law. Some Bay Area cities (Santa Cruz, Oakland) have added local incentives with higher size allowances.
Quartz Construction & Remodeling (CSLB #1003436) designs and builds ADUs throughout the Bay Area, navigating each city’s specific setback and zoning requirements. Call (650) 749-7436 for a free ADU feasibility assessment — we’ll determine what you can build on your specific lot and at what cost.
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